The Cosmic-Ray Electron and Positron Spectra Measured at 1 AU during Solar Minimum Activity

We report on a new measurement of the cosmic-ray electron and positron spectra. The data were collected by the balloon-borne experiment CAPRICE94, which was flown from Lynn Lake, Canada, on 1994 August 8-9 at an altitude corresponding to 3.9 g cm-2 of average residual atmosphere. The experiment used the NMSU-WIZARD/CAPRICE94 balloon-borne magnet spectrometer equipped with a solid radiator Ring Imaging Cerenkov (RICH) detector, a time-of-flight system, a tracking device consisting of drift chambers and multiwire proportional chambers, and a silicon-tungsten calorimeter. This was the first time a RICH detector was used together with an imaging calorimeter in a balloon-borne experiment. A total of 3211 electrons, with a rigidity at the spectrometer between 0.3 and 30 GV, and 734 positrons, between 0.3 and 10 GV, were identified with small backgrounds from other particles. The absolute energy spectra were determined in the energy region at the top of the atmosphere between 0.46 and 43.6 GeV for electrons and between 0.46 and 14.6 GeV for positrons. We found that the observed positron spectrum and the positron fraction are consistent with a pure secondary origin. A comparison of the theoretically predicted interstellar spectrum of electrons shows that the injection spectrum of primary electrons is steeper than that of the nucleonic components of cosmic rays. Furthermore, the observed electron and positron spectra can be reproduced from the interstellar spectra by a spherically symmetric model for solar modulation; hence, the modulation is independent of the sign of the particle charge.

[1]  M. Casolino,et al.  New Measurement of the Flux of Atmospheric Muons , 1999 .

[2]  M. Casolino,et al.  The Cosmic-Ray Proton and Helium Spectra between 0.4 and 200 GV , 1999 .

[3]  A. Strong,et al.  Production and Propagation of Cosmic-Ray Positrons and Electrons , 1997, astro-ph/9710124.

[4]  G. Tarlé,et al.  The Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation , 1997, astro-ph/9712324.

[5]  M. Casolino,et al.  The Cosmic-Ray Antiproton Flux between 0.62 and 3.19 GeV Measured Near Solar Minimum Activity , 1997 .

[6]  Peter Meyer,et al.  Solar Modulation of Cosmic Electrons , 1996 .

[7]  Davis,et al.  Measurement of 0.25-3.2 GeV antiprotons in the cosmic radiation. , 1996, Physical review letters.

[8]  M. Casolino,et al.  Performance of the CAPRICE RICH detector during the 1994 balloon flight , 1996 .

[9]  V. Bidoli,et al.  The WIZARD / CAPRICE silicon - tungsten calorimeter , 1996 .

[10]  M. Simon,et al.  Measurement of the Positron to Electron Ratio in the Cosmic Rays above 5 GeV , 1996 .

[11]  Knapp,et al.  Cosmic ray positrons at high energies: A new measurement. , 1995, Physical review letters.

[12]  V. Bidoli,et al.  WiZard SiW imaging calorimeter: a preliminary study on its particle identification capability during a balloon flight in 1993 , 1995 .

[13]  T. Wyatt,et al.  Where to stick your data points : the treatment of measurements within wide bins , 1995 .

[14]  A. Morselli,et al.  Observations of cosmic-ray electrons and positrons using an imaging calorimeter , 1994 .

[15]  T. Francke,et al.  Results from beam tests of the CAPRICE RICH detector , 1994 .

[16]  R. Golden,et al.  Performance of drift chambers in a magnetic rigidity spectrometer for measuring the cosmic radiation , 1994 .

[17]  V. Bidoli,et al.  A silicon imaging calorimeter prototype for antimatter search in space: experimental results , 1993 .

[18]  V. Bidoli,et al.  Performance of a balloon-borne magnet spectrometer for cosmic ray studies , 1991 .

[19]  P. Evenson,et al.  Solar Modulation of Cosmic Electrons: Evidence for Dynamic Regulation , 1991 .

[20]  J. Jokipii,et al.  Heliospheric Effects on Cosmic-Ray Electrons , 1991 .

[21]  D. Mueller,et al.  Cosmic-ray positrons from 10 to 20 GeV - a balloon-borne measurement using the geomagnetic east-west asymmetry , 1987 .

[22]  R. R. Daniel,et al.  A measurement of the absolute flux of cosmic-ray electrons , 1984 .

[23]  R. Protheroe On the nature of the cosmic ray positron spectrum , 1981 .

[24]  R. Golden,et al.  A magnetic spectrometer for cosmic ray studies , 1978 .

[25]  C. J. Pellerin,et al.  Cosmic-ray positron and negatron spectra between 20 and 800 MeV measured in 1974 , 1976 .

[26]  G. Smoot,et al.  Measurement of primary cosmic-ray electrons and positrons from 4 to 50 GeV , 1975 .

[27]  R. Hartman,et al.  Measurement of cosmic ray positron and negatron spectra between 50 and 800 MeV , 1975 .

[28]  R. R. Daniel,et al.  Cosmic-ray-produced electrons and gamma rays in the atmosphere , 1974 .

[29]  P. J. Schmidt Cosmic-ray electron spectrum and its modulation near solar maximum , 1972 .

[30]  J. D. Sullivan GEOMETRICAL FACTOR AND DIRECTIONAL RESPONSE OF SINGLE AND MULTI-ELEMENT PARTICLE TELESCOPES. , 1971 .

[31]  R. Hartman,et al.  Charge composition and energy spectrum of primary cosmic-ray electrons , 1969 .

[32]  R. R. Daniel,et al.  Electron Component of the Primary Cosmic Radiation at Energies ≳15 GeV , 1965 .

[33]  P. Meyer,et al.  RATIO OF ELECTRONS TO POSITRONS IN THE PRIMARY COSMIC RADIATION , 1964 .

[34]  R. Vogt,et al.  Electrons in the Primary Cosmic Radiation , 1961 .

[35]  J. Earl Cloud-Chamber Observations of Primary Cosmic-Ray Electrons , 1961 .